A device of a programmable logic controller is a memory that is provided in the programmable logic controller to store therein data of information primarily related to manufacturing, such as control information of a machine tool and a manufacturing apparatus and recipe information including the temperature or mixing ratio of materials in an apparatus.
A user can freely perform writing and reading of data to/from the device using a computer in which a programming tool or a monitoring tool of the programmable logic controller is installed or using other external input/output devices compatible with the programmable logic controller. The writing and reading can be similarly performed via a network by use of an information system unit or the like.
Reading and writing of data can be also performed from/to the device of the programmable logic controller by a program that runs on the programmable logic controller using a device read command or a device write command, apart from the tools mentioned above.
A control method of a manufacturing apparatus using a programmable logic controller and a manufacturing method of products using the manufacturing apparatus are generally recorded in a device. Such information is know-how of each of manufacturers of manufacturing apparatuses and is often information classified as secrets by the manufacturers of the manufacturing apparatuses.
Meanwhile, as for the device, anyone can freely access any device through the tool or the program. In addition, data recorded in the device may be changed by an erroneous operation.
Patent Literature 1 discloses a programmable logic controller peripheral device, including an encryption unit that encrypts authentication data for authenticating whether to permit a communication to the programmable logic controller with respect to data used in the programmable logic controller.